The overall aim of this project is to develop a gene transfer procedure to repair or replace neurotransmitter function in aged cognitively impaired animals, with the idea that the tools and strategies developed and tested will be relevant for the treatment of Alzheimer~s Disease (AD). Two neurotransmitter systems will be examined that are consistently involved both in AD-related neuronal degeneration, and in processes of learning and memory. The hypothesis underlying this proposal is that the transfer of genes to the brain will either protect against age-related neuronal degeneration, or replace missing neuronal transmitter function. Consecutively, these therapeutic strategies will delay age-related function decline or reverse some of the deficits associated with age-related cognitive decline. Specifically, we plan to use ex vivo gene transfer techniques to determine if Nerve Growth Factor (NGF) delivery to different parts of the cholinergic basal forebrain (CBF) system can improve deficits in aged cognitively impaired animals. We then plan to determine the duration of NGF expression required for long-term functional improvement in aged cognitively impaired animals. As related to the cholinergic system specifically, we will determine whether acetylcholine (Ach) releasing cells grafted into different target areas of the CBF system improve cognitive deficits in aged cognitively impaired animals. Then we will determine methods for, and the importance of, regulating the expression of choline acetyltransferase (ChAT) and the release of acetylcholine (Ach) from cells that are genetically engineered to secrete Ach, when these cells are implanted in the cortex an hippocampus of aged rats with cognitive impairments. With a new transmitter system and animal model we will determine if layer II entorhinal cells, which are damaged and lost in age, cognitively impaired rats, can be preserved or restored by basic Fibroblast Growth Factor (FGF-2). Finally, in regards to in vivo gene transfer, we will compare vectors for the direct delivery of therapeutic genes by viral (adenovirus, adeno-associated virus, and modified human immunodeficiency virus) infection into the adult and aged brain.